tbh people mock harry for going back to rescue fleurs sister in the second triwizard task but harry knows dumbledore better than anyone else. he probably looked at the situation and thought “would dumbledore let an eight year old drown just because fleur couldnt do this bit? yes. yes he would.”
it’s also possible he was acting off of the lessons he learned in the abusive dursley household. that’s why he does a lot of his so-called “hero complex” shit. he takes a lot of personal responsibility for other people bc he learned growing up that “no one’s here for you, no one will help you, you will not catch any breaks”. he helps bc if he didn’t, who would? certainly not the dursleys, and that’s what he grew up with.
he does things by himself and the two people he actually trusts, bc he’s learned that authority figures are no help and will only make things worse. he takes situations at face value bc he’s never seen other options in his life, he’s never HAD other options in his life. speaking very personally, that was a serious marker of abuse that i saw in myself – i never thought abt escape, or what i could do to improve my situation, bc i didn’t even see that as an option. the options were survive or don’t, deal w it or don’t, acclimate or implode.
maybe he wasn’t thinking abt what DUMBLEDORE would do, what anyone at hogwarts would do. maybe he was acting off what he knew the dursleys (his main authority figures) would do. the dursleys would let the girl drown. and harry was there, and harry could do something, and so harry did. he took personal responsibility for fleur’s sister’s safety bc all his life he’s learned that authority figures cannot be trusted to do so.
people characterize these aspects of harry as a “hero complex” or a “stupid nobility” or a “lack of common sense”, but i don’t agree with that. i can’t put my finger on exactly what it is. it’s not completely unhealthy; it’s even very useful and responsible on occasion.
it’s called “complex ptsd” and if you get out of the abusive situation before you’re old enough to understand how fucked up it was, like Harry did, you don’t end up with the classic flashbacks so much, just atypical behavior patterns and a high risk of other shit. That’s why Harry is so fucked up by everything that Umbridge does, it’s because he’s being retraumatized in his safe space.